1. Field of the Invention
This invention relates generally to circuit breakers and, more particularly, to circuit breakers including a magnetic trip mechanism.
2. Background Information
Circuit breakers having an operating mechanism and a trip mechanism, such as a thermal trip assembly and/or a magnetic trip assembly, are known in the art. An example of such circuit breakers is disclosed in U.S. Pat. No. 5,805,038, which is incorporated by reference herein. The trip mechanism is automatically releasable to effect tripping operations and manually resettable following tripping operations. Such circuit breakers, commonly referred to as miniature circuit breakers, have been in use for many years and their design has been refined to provide an effective, reliable circuit breaker, which can be easily and economically manufactured on a large scale. As such, the ease of manufacture of such circuit breakers is of importance.
Circuit breakers of this type include at least one set of separable contacts disposed within a non-conductive housing. Typically, there is a fixed contact attached to the housing and a movable contact coupled to an operating mechanism. The operating mechanism includes a movable operating handle that extends outside of the housing. The operating handle has essentially three stable positions: on, off, and tripped. The operating mechanism further includes an operating arm, upon which the movable contact is disposed, the trip mechanism, and a cradle. The cradle is coupled to a spring and is disposed between the trip mechanism and the operating arm.
The trip mechanism may include a thermal trip capability, which responds to persistent low level overcurrents, and/or a magnetic trip capability, which responds instantaneously to higher overload currents. One such trip mechanism includes a cantilevered bimetal member, a magnetic yoke and a magnetic armature. The magnetic yoke is a generally U-shaped member secured to the bimetal member at a bight portion of the magnetic yoke with legs thereof facing the armature. The magnetic armature is secured to a supporting spring that is, in turn, secured at its lower end near a free end of the cantilevered bimetal member. Thus, the armature is supported on the bimetal member by the spring. The armature has a window opening through which one end of the cradle extends. A latch ledge on the cradle engages the edge of the window to latch the latchable operating mechanism in the latched position. The trip mechanism includes three welds: (1) between the bight portion of the magnetic yoke and the bimetal; (2) between the lower end of the bimetal and the lower end of the spring; and (3) between the upper end of the spring and the lower end of the magnetic armature. This assembly procedure is time consuming. Furthermore, the welds are subject to failure.
There is, therefore, a need for a circuit breaker trip assembly, which reduces manufacturing time and/or cost.
There is a further need for a circuit breaker trip assembly, which minimizes a count of welds and/or improves reliability.
There is room for improvement in circuit breakers.